In a tandem-type image forming apparatus including a plurality of image forming units, a so-called color shift may occur in which relative positions of toner images of different colors formed on image carriers of the image forming units are shifted in a scanning direction (main scanning direction) of light irradiated from a laser scanning device to the image carriers. For example, in this type of image forming apparatus, the color shift may occur due to expansion and contraction of optical members that are caused by the temperature change in the apparatus. As a result, a color shift correction for correcting the color shift may be executed in the image forming apparatus. In particular, a color shift correction using different correction tables for a temperature increase and a temperature decrease in the image forming apparatus may be executed (see, for example, PTL 1).